The claimed invention is a method and apparatus for detachably joining two members and, in particular, for joining two members through the use of a movable wedge means.
The technical problems associated with joining two members to form a solid connection have been known for many centuries. These problems are compounded when it is also desired to have the capability of disassembling the two members non-destructively. Further technical problems are introduced when the objective is not merely to detachably join two members but also to provide wide distribution of forces along the joined edges, or to provide a fluid seal at the joined edges, or to join the edges without substantial longitudinal movement, or to transmit rotational torque across the joint.
A complete discussion of the various techniques developed over the years for addressing one or more of these objectives would encompass many volumes of technical information and thousands of prior patents. However, there are three basic techniques which are of particular interest in conjunction with the present invention. These may be referred to in terms of the mechanical structures which may be used to create joining forces between the two members: (1) the wedge, (2) the screw, or (3) the cam.
There are two ways a wedge can be used to detachably fasten two members. The first is by means of a jam fit, where the wedge is forced between fixed members to take up the slack in an otherwise loose fit. In these applications, the components forming the joint are placed in compression. One example of this form of detachable joint is the wedge clamp illustrated in FIG. 1 which is used on the work benches of carpenters.
In prior art FIG. 1, two rails 1 and 2 are fixed to a work bench 3 and wedge 4 is advanced in the direction of its apex to retain work piece 5 (first member) against rail 2 (second member). While this technique results in a firm connection between the corresponding edges of work piece 5 and rail 2, the connection is directional. Longitudinal forces along the edges in one direction will tighten the joint while forces in the opposite direction will cause detachment. This type of wedge joint is also characterized by longitudinal displacement along the edges of the two members as they are being joined. As will be discussed below, this is a significant disadvantage in many applications.
The second way a wedge can be used to detachably join two members involves placing a portion of one member in tension. This second technique has also been employed in carpentry, as illustrated in FIG. 2, where first member 6 includes through mortise 7 and second member 8 has extended tenon 9 with wedge 10 inserted into opening 11 through tenon 9. This method has been used in trestle tables and in post and beam construction. The two members are joined by driving wedge 10 into opening 11 thereby placing tenon 9 in tension and drawing second member 8 firmly into contact with first member 6. While this form of wedged tenon joint is quite strong in opposing forces exerted along &:he central axis of the two members, the joint is notoriously poor with respect to pivotal or shear forces exerted between the two members.
Similar prior art applications where a wedge has been used to join two members are described in U.S. Pat. No. 544,823 (a wedge used to attach a side rail to a bedpost); U.S. Pat. No. 1,542,888 (a wedge used to hold a framed screen in place over a window); and, U.S. Pat. No. 1,877,263 (a wedge used to secure the sliding door on a boxcar in position during transit).
The screw is often likened to a wedge because, fundamentally, both structures incorporate inclined planes to gain mechanical advantage. However, the screw is quite different from the wedge because a screw joint (between two members, such as a jar and a screw-on cap) requires rotational motion between the two members being joined. As the cap is tightened, the upper edge of the jar engages the inside of the cap to form a line or annular surface of contact. Friction between the first member (jar) and the second member (cap) makes closing or opening the jar difficult. The relative motion between the two members may also distort or damage gasket material placed between the cap and the jar, leading to a loss of sealing integrity after only a few uses. The amount of friction encountered in joining two threaded members is proportional to the length and pitch of the thread. In many cases this inherent friction makes connection and disconnection difficult.
The fact that screw joints require substantial rotational movement between the two members being joined often adds difficulty, especially where the two members are long, flexible or resilient, since the rotational motion required to make the connection may lead to misalignment, kinking or complex handling of the members. In addition, the frictional forces created between the moving surfaces being joined in a screw connection can be so great as to impede or prevent rotational movement in the opposite direction which is necessary to disengage the two members. This is often observed in the case of jars with threaded caps where the pitch of the thread is low to allow positive resealing but where this low pitch allows overtightening with resulting difficulty in later removal of the cap.
A cam is also frequently likened to a wedge. However, because a cam requires relative motion between the members being joined it shares many of the disadvantages associated with a screw. A common example of two members being joined through the use of a cam is the pressure cap detachably joined to the filler neck on an automotive radiator. In operation, the radiator cap is rotated relative to the filler neck. Portions of the cap engage cams on the filler neck and the pitch of the cams draws the cap down firmly over the top edge of the filler neck. The cap moves relative to the neck even after contact is made, abrading the components and often distorting the sealing gasket typically located between these two joined edges. To overcome the problems associated with friction contact and relative motion between the edges, intermediate rotational elements have been used, adding further complexity to the joining and sealing of the cap.
A screw type attachment mechanism, depending on the thread pitch, may require several complete rotations of one of the members to effect complete attachment. In the production or use of a variety of goods, this is needlessly time consuming. This inefficiency can be lessened through use of a cam connection where one member is rotated less than one complete revolution. While the process of assembly or disassembly is faster, because fewer turns are required, the friction and displacement between the two members being joined still present many disadvantages.
Caps for jars or containers which are intended to be sealed typically employ either a screw type mechanism or a low pitch cam. With the current need for "child-proof" caps, clutch mechanisms and variable pitch cams are also employed. In all cases, however, the problem remains of the cap and jar binding during the last stages of the attachment. This not only wears the seal but also increases the force required to close or to reopen the container, often to the point where weak, aged or infirm people are unable to remove the stuck cap.
In view of the foregoing, it is therefore an object of the present invention to provide a method and apparatus for detachably joining two members without having substantial displacement between the two members along their respective edges of contact.
Another object of the present invention is to provide means for detachably joining two members and thereafter transmitting substantial torque or shear across the joint without relative motion between the edges of contact.
Another object of the present invention is to provide a means for releasably sealing the joint between two members.
Another object of the present invention is to provide an improved cap or closure for jars, containers or enclosed volumes.
Another object of the present invention is to provide a method and apparatus for detachably joining two members of circular section wherein connection is accomplished through the movement of a wedge means through a turn of less than 180.degree. while the two members themselves do not rotate relative to one another during or after attachment.
Another object of the present invention is to provide a method and apparatus for detachably joining two members by the exertion of predetermined forces between the two members being joined.
Another object of the present invention is to detachably join two members along their respective edges through the exertion of forces distributed among a plurality of points along the edges being joined.
Another object of the present invention is to axially join and detach two members of circular cross-section without substantial rotational movement between the two members.
Another object of the present invention is to provide a kit of components suitable for connection to two linear or circular members for the purpose of detachably joining the two members along their corresponding edges.